The effect of F −-doping and temperature on the structural and textural evolution of mesoporous TiO 2 powders

Abstract

Mesoporous F −-doped TiO 2 powders were prepared by hydrolysis of titanium tetraisopropoxide (TTIP) in a mixed NH 4F–H 2O solution. Effects of F − ion content and calcination temperatures on the phase composition and porosity of mesoporous titania were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and BET surface areas. The results showed the BET surface area ( S BET) of the pure and doped powders dried at 100°C ranged from 260 to 310 m 2/g as determined by nitrogen adsorption. With increasing calcination temperatures, the S BET values of the calcined titania powders decreased due to the increase in crystalline size. The pore size distribution was bimodal with fine intra-particle pore and larger inter-particle pore as determined by nitrogen adsorption isotherms. The peak pore diameter of intra-particle pore increases with increasing F − ion content. At 700°C, all the titania powders exhibit monomodal pore size distributions due to the complete collapse of the intra-particle pores. The crystallization of anatase was obviously enhanced due to F −-doping at 400°C and 500°C. Moreover, with increasing F − ion concent, F − ions not only suppressed the formation of brookite phase at low temperature, but also prevented phase transition of anatase to rutile at high temperature.